Rojan Pirsalehi's oesophagus was damaged after she swallowed a battery and the acid inside leaked out. Photograph: Hemmat Khahi

Rojan Pirsalehi is a four-year old girl who desperately needs life-saving surgery on her oesophagus. But that is not the extent of her predicament. Rojan's biggest problem is that she is Iranian, and the hospital most likely to save her life is in the capital of one of Iran's great enemies: Britain.

At the age of two, Rojan swallowed a battery from her father's car radio remote control. The acid inside gradually damaged her entire oesophagus, her mother, Mozhgan Elmipour, said.

"When I realised what had happened, I instantly took her to the hospital but they refused to help her urgently," she told the Guardian. "We were told that it wasn't a serious problem but at the time when they found that the battery's acid had caused serious damage it was too late to save her oesophagus."

After surgery, Rojan's oesophagus was ultimately removed except for few centimetres. But the lack of medical expertise and necessary facilities in Iranian hospitals means that her parent's only hope for her recovery is to send her to London's Great Ormond Street hospital. Rojan's previous operations in Iran have not been entirely successful and she can only be fed liquids through a syringe.

But her family face a tough odyssey to reach London. Raising money for an operation which would cost the parents more than 300 times their £250 a month salary is only one complication. The bigger conundrum is how to arrange for a medical visa for a country that has removed its diplomatic presence from Iran.

Last November, Britain withdrew all staff from its embassy in Tehran after a group of protesters stormed the mission, ransacking offices and diplomatic residences in a demonstration believed to have been organised in reaction to UK's decision to sever all financial ties with Iran's banking system.

In response to the attack, Britain shut down the Iranian embassy in London and expelled all of its diplomats. Iran's foreign ministry was embarrassed by the attack, which is believed to have been carried out by hardliners close to the country's supreme leader rather than those sympathetic to the government.

Rojan's case represents the difficulties that ordinary people face in such a situation, especially those in need of consular assistance.

Iranians have complained in recent years that western sanctions against the country, imposed in the hope of forcing the authorities to open their nuclear facilities to UN inspectors, have prevented ordinary people from getting medical supplies or even essential plane repair parts. Scores of people have died in plane crashes in Iran in recent years.

"My passport is expiring soon and I don't know how to extend it without going back to Iran," said Reza, a university student in London, who didn't want his full name published.

Elham Mehrabi, who has recently given birth, says her mother couldn't come to London from Iran to take care of her during her pregnancy and afterwards because of visa issues.

"We had arranged everything for her to come and take care of me when the baby was due to born and all our plans were ruined after the embassy attack because it was no way for her to apply for a visa from Tehran," she said.

For Rojan, an operation in London could be life-saving. "In the past two years, my family has been under all sorts of financial and psychological pressure to find a way to bring her to the UK for an operation which can save her life and we haven't yet been successful," said her mother.

Great Ormond Street Hospital said it "often get requests from families abroad to see if we can treat their child".

"A gastric pull up is an operation that can be carried out on someone who does not have an oesophagus. During such an operation a patient's stomach is repositioned and attached directly to their throat," a hospital spokesperson said.

The hosiptal was not, however, in a position to comment on whether the treatment was appropriate way forward for Rojan without being able to examine her. "As with all potential overseas patients we would need to follow all the correct and proper administrative processes before moving forward."